Measure California’s Water

California’s water board voted Tuesday to impose new rules that would reduce the state’s urban water use by 25 percent, as mandated by Gov. Jerry Brown at the beginning of April. By requiring towns and cities to cut back, the state expects to save about 1.3 million acre-feet of water over the next nine months. Rationing in urban areas will be tiered. Cities and towns that have already been conserving water will not have to cut as much as areas that have not.

But the state has yet to address another big problem: Its system for allocating water from rivers and streams — an essential tool for regulating agricultural water use in the state — is not up to the challenge of dealing with a major drought. For one thing, this system does not similarly reward conservation.

In times of drought, the state board cuts off water-rights holders in reverse order of seniority, not based on how much water they use. And even if the board wanted to move to a use-based system, it does not have anything close to up-to-date information on how much water each rights holder is actually drawing. Those whose rights predate 1914 must report their monthly use every three years; those with rights newer than 1914 must file annually.

Even those numbers are not reliable. Rights holders who don’t use all the water they are allowed could have their allocations lowered in the future, which gives them an incentive to overreport their use. Even if they don’t consciously overreport, not all agricultural users have the technology needed to measure their water use accurately. And reports filed at one- or three-year intervals don’t tell the water board who’s using the most water now.

If the state required accurate, near-real-time data from all rights holders, the board could identify those rights holders who are using the most water and restrict their use. It could also issue partial water restrictions rather than cutting rights holders off entirely. Such a system would encourage users to conserve to avoid harsher reductions. It could free up more water for cities, fish and wildlife. It might even make more water available for some agricultural water-rights holders if those putting the heaviest burden on the watersheds are restricted.

A rational system along these lines would not require major changes in the laws governing water use, according to a 2014 paper by Theodore Grantham, a research biologist for the United States Geological Survey, and Joshua Viers, a watershed scientist at the University of California, Merced.

Droughts in California may become more frequent, and their effects more severe, as the state feels the effects of climate change. The state can’t respond to them if it doesn’t know who is using how much.